Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Inside the human body lives a large number of symbiotic microbes, among which the gut microbiota acts asan important environmental factor to host health. There are more than 1000 species of bacteria, whose number exceeds 10 folds of the number of human cells, and whose gene number is about 150 folds of that in human cells. In this context, the human body as a “superorganism” made of host cells and symbioticmicrobes including gut microbiota, and the genome encoding a consortium of gut microbes (microbiome) is considered as the second human genome, also known as “humanmetagenome”. When human health status changes, the composition of symbioticmicrobes changes accordingly. Conversely, changes in the composition of symbioticmicrobes lead to the change in the human health status. Together, the diversity in human genome and the genome of gut microbiome affects immunity, nutrition, metabolism, and the health and disease status of the human host. However, up to now, it is not clear by what mechanisms the gut microbiota contribute to disease etiology and pathology, which type of bacteria is positively correlated with the health status of the host, and which type of bacteria is negatively correlated with the health status of the host.